The purpose of this work is to determine the mechanism by which certain fungal metabolites containing isolated five-membered rings are biosynthesized. The metabolites in this study are brefeldin A (1) and jasmonic acid (2). Because it is most likely the case that these molecules are biosynthesized from acetate or fatty acids, there is the likely possibility that the mode of formation of the cyclopentane moiety resembles that of the prostaglandins. The long-term goal of this work, then, is to assess the generality in nature of such a mechanism. The work will involve several approaches: 1) assessment of the role and origin of oxygen atoms in the cyclization process by conducting experiments in an atmosphere containing O18 2/O16 2, 2) the relative importance of fatty acids vs. acetate as precursors, 3) detection of intermediates which fill in the pathway between precursor and product, 4) synthesis and feeding of suspected intermediates. Initial work has begun on brefeldin A and it is anticipated that work on jasmonic acid will begin shortly. Ultimately, we expect to initiate studies on enzyme specificity.